1. Field of the Invention
The present invention pertains to water-based printing inks, or aqueous inks, which are particularly suitable for flexographic and/or intaglio printing and exhibit improved deinkability. It is the object of the invention to provide printing inks of the type mentioned which may be classified as anion-based aqueous printing inks.
Reconditioning of printed waste paper by deinking is gaining increasing commercial importance. Deinking of waste paper by the flotation method is particularly important. In this connection, it is known that oil-based printing inks from newspapers, magazines, catalogs, telephone directories and the like are relatively easily deinked. It is further known, though, that prints consisting of aqueous flexographic and intaglio inks are poorly deinked by the flotation method if the printing inks or the binder systems employed are anion-based. Such binder systems and printing ink types, desirable as such for a number of reasons, will result in very small pigment particles upon deinking, particularly with the flotation method, and hence in unacceptable losses in whiteness of the printing substrate. In order to achieve sufficient deinking results, such waste paper prints had to be deinked by the so-called washing method. However, this method will result in high losses of fillers and short fibers, so the yield of recyclable paper mass will be less and the effluent contamination will be markedly higher than they are in the flotation method.
2. Discussion of Related Art
Technical publications, including the most recent ones, confirm the difficulties described herein. There may be mentioned the publication by W. Forster et al., "Bestandsaufnahme der Deinkbarkeit von bedrucktem Altpapier" in Wochenblatt fur Papierfabrikation 8, 1992, 281-285. The authors confirm their results already achieved in former studies, i.e. that newspapers which have been prepared by flexographic printing using water-based flexographic printing inks will yield but very low deinkability figures, cf. supra, page 281, abstract, and page 284, relating to flexographically printed newspapers.
A similar statement is found in the publication by H. U. Suss et al., "Das Papier", 55th volume, No. 3, 1991, 89-96. It is set forth introductorily in the abstract that water-based printing inks are not separated by flotation in the conventional deinking process. To solve this problem, a two-step, alkaline-acidic flotation of printing inks which are hardly removed from waste paper has been proposed. In the acidic flotation step, quaternary amines having at least one long-chain alkyl residue, e.g. hexadecyltrimethylammonium chloride, are to be used as additives. Quaternary ammonium compounds of this type are known to exhibit significant drawbacks, especially in ecological terms. They have increased toxicity to fish and are hardly degradable.
To overcome the problems set forth hereinbefore, DE-A 1 41 15 731 has proposed deinkable aqueous inks the essential feature of which is the use of water-dilutable cationic resins as the binder component. Water-dilutable cationic acrylic resins in the form of a dispersion are preferably employed as binders. The examples of this latter reference include a comparative example in which a water-based printing ink comprising an anionic acrylic resin as the binder (printing substrate: newspaper) actually results in no measurable deinkability in the flotation method.
The teaching according to the invention proceeds from the object to provide anion-based systems and corresponding water-based printing inks which will give good printing results in practice, in particular in flexographic and/or intaglio printing, without problems and which nevertheless will give a printed matter which can be effectively deinked even in the flotation method and hence will result in high-quality secondary products.